Telephone system



April l0, 1928.

A 1,665,338 W. WHITNEY TELEPHONE SYSTEM Filed OCT.. 19. 1926 4Sheets-Sheet TWO Fl. )$31.4 Z

April 1o, 192s. 1,665,338

W. WHITNEY TELEPHONE SYSTEM Filed Oct. 19. 1926 4 Sheets-Sheet 2 EMM I'April 10, 1928. 1,665,338

W. WHITNEY TELEPHONE SYSTEM Filed Oct. 19. 1926 4 Shee Patented Apr.Al), 1928.

nai-rsa sierras retina:

rarest 'or sie WILEY WHITNEY, or 'nasr online-n; new:rnnsnryessreno'R-To BELL TELEPHONE;

, neBonAmon-ns,

' rolex.

TELEPHONE. SYSTEM.

. 'Appiicganon fired october 19, 1926; ser1a1-N-.f142,557

This invention relates to ytelephone {systems and more particularly toimprovements in emergency listening circuits to be used` in common. withdifferentl types between- Inanual exchanges.4

. According to this invent-ion, an emergency listening circuit isarranged to vhe' interchangeably used'. inthe establishing fof conAnections involving such trunks as'4 AB trunks, tandem completingltrunks, or toll switching trunks or other connecting trunks havingsimilar characteristics which are operated on f the so.calledystraightforward basis. Infti'unks o'lthese` various types differentcircuit conditions are encountered and this circuit is designed'topreventinter:

ferencejand false :signaling when it becomes necessary to.y employ ancircuit..` y i '.Wfhcn. Ythev emergency ,listeningv circnit, yaccordingto another aspect of the invention,

is usedf in connectionwith. an AB or tandem.

completing* trunk connection, when the a-utomatic listening Varrangementis not functioning properly. the application'of a signal over thel trunkis prevented.. Accordingly means is provided in this emergency listen-`ing circuit whereby, Whenit isi connected to an' established trunkconnection ofeither ofi thcsetwo ytypes the supervisory relay in thetrunk circuit is operated only forl a coinparat-iyely short period,Whichfisl insufficientl tov cause any current changes to takevplace atthe` distant end ofthe trunk.

whereby the sifip'eryiscry relavin theftolly switching trunk'isoperatedand maintained operetedl afi-'long as the `connection to the encylistening vcircuit remains. ,The ltion of the sleeveV relayinthe toll ofconnections emergency listeningl K n The ring ing trip` relay in thetrunk will. also be actn-` :ase of the use of the emergency switchingtrunk, which ordinarily starts the machine ringing, is thereby preventede from.

having such an eect. v

j This invention has been illustrated inthe accompanying drawings inWhich Fig.r` l" showst-he incoming end of an AB or tandem completingtrunk for' straightforward" trunk connectionsV and portion of a. commonse` quence circuit having part of a! listening c ircuit for,automatically connecting the trunk',

eperators telephone sctto the incoming end.

inconro'niirnn or nsw-renner. .-YWA ooBronArIoNrOF NEW civ-the trunk, ofa, group ofy trunks, overl` I While Figs. 2 andV 3 show` a tolloperators telephone set," the remainder .of the. listeningcircuit'arrangenient for supervising the cony neet-ion and associatingthetol'loperators telephone set through the. sequence circuit tov theengaged trunk and also an emergency listening circuit associated;therewithydee signedqin accordance .WithA this invention; Fig. 4fillustrates the `incomingfend of aftoll.,- switching trunk of' thestraightforvvard type `and a portion of a sequence circuit` identicalwith that shown in Fig.. 1. This circuit maybe used -inA connectionWiththe automatic listening goil-cuit and the emergency listeningcircuitshown' in Figs. v2 and 3 and' connected thereto in the samemanner v as the circuit shown lin Fig. lg isconnected. With thesecircuits. Fig. shows the man-` ner lof'arranging the Figs. 1 to forreadir'igv of thecircuits .y f, v'In the following detaileddescriptionolf the invention 4it Willi-be. assumedV that the`emergency,,listening circuit 'shown yin Figs. 2 and 3 Will be requiredin clearing calls Vincomingover the d'fiii'erent types of'trunls shownLin Figs. l and` 4.5 It isWjell-knownin the art howjtrunks'ofthese'types mayV be y V-used forVV completing connections from an ,At board,from a tandem ofticeor `from a toll liner overa toll switching 'trunkWith out the-.use of call Wire circuits.` It Will.

thereforecnly bei-necessary to describe as;l

muchoif the, operations Vof these trunk connections aswill berequired-to fully vunderstand the conditions that. anKV emergency lise.

teninn circuit, designed in accordance With thil inventionencounters-'When v1t becomes these'types. of trunks. e i ythe AB trunk Ashown in Fig. 1, or in. a similar trunk such as .a tandem completyet; Y

to employ: it connections of" ing trunk, it may be assumed that relay 1is actuatedto signal a trunk operator at i whose board the incoming endof this trunk terminates.k When this relay operates a circuit is closedfor the operation of relay 2 y througliltheleft-hand winding of thisrelay and `the' inner right-hand armature of Vrelay y 3. The operationof relay 2 closes a circuit rfor Vthe operation of relay 3 as follows:Battery, left-hand winding` of `relay 3,V rightn handV winding' andinner right-hand armature-and frontcontactrof relay 2, `.lower armatureand back Vcontactl and lowerf winding of relay `l to-ground. Relay 3 inoperatingv closes a locking circuit for itself through its right-handarmature and front contact under control of relayl, while the originalvenergizing circuit for relay 2` is Opened.

This relay VVis, however,` now maintained locked through its right-handwinding over thel above mentioned circuit"through theY lower winding ofrelay 4.

'i Theoperation ofrelays 2 and 3 causes the guardv and disconnect lamp 6to be lighted;V

overa' circuit as follows: Battery, lampV 6,

outer right-handarmature and front contact of relay 3, `outer right-handarmature and front Contact of relay 2 through a resistance .to ground.VThe automatic listening circuit comprising the sequence circuit shownin the lower.: part of Fig. `1 and the central circuit in Figs. 2 and 3functionto connect the operators ytelephone set' 300 to trunks such y asA in a predetermined sequence. When therefore relay 2 is operated acircuit is closedV for the operationV of relay 7, of the groupof'relays'? and 8 in the sequence circuit! that are individual vto trunkA. .This

Y circuit `may lbe traced as .-follows: Battery,

right-hand Varmature and bac-k contact of re- Y lay" 200, winding ofrelay 7 ,left-hand armature-and lfrontcontact of relay 2 to ground.

The Voperation ofrelay 7 closes acircuit `for if the operation ofrelaysSand 301 as follows:

Battery, relay 8, lowerA outer armature and` 'front' contact of relay 7left-hand Varmature and back contact of relay 200, vwinding of relay301, armature and back contact of re- 'v Vlay3031toground. Relay 3D1-inoperating closesan :obvious circuit for the, operation of relay 303which opensthe original energizingmcirciiit of relay 30,1.andextends'this circuit tofgroundthrough theleft-hand ari matureandfrontcontactof relayv 301., The

operation'` of relays 7 and 8 in the sequenceV circuitv prevents, asiswell'known lin the art,

any-other relays corresponding to 7 and 8,4

.. individual yto other trunks, from operating when attempts are madetoL establish such connections. The operation of relays 7 and "SleXtendsthe individual .leads 9, 10,711, 12

and'13 to4 the 'controlcircuit shown in Fig. 3.

The extension of lead 13 causes certain re- Y i i* laysfin the cont-rolcircuit to operate to connect a-tone'to the trunk A and closes acirvofrelay 8, outer right-'hand armature and front contactl of'relay 3, outerright-hand front contact of relay 2 to ground; It willv be noted-that ifthe operator-s .telephone set 300 is connected through the plugsandjacks shown in VFig. 3 to the control circuit,.relay 307 will beoperated and if this relayis op elated, the Vcircuits .for actuatingandmaintainingrelay'sj308 and 309v are closed and as will behereinafterdescribed, relay 315 rwill f j also be operated so that the abovementioned circuit 'for relay llis therefore closed at this time. Theoperation of relay 15 lights ,the pilot lamp-17 whicliris associatedwith the groupof trunks served by the sequencecircuit shown in Fig. 1.This pilot lamp lights only when a trunk in this group is connectedtothe control circuit. y

v rllie'circuit'for lighting of lamp 6is eX- l tended as shown throughthe winding of re- .lay 304V to battery but tlie'resistance ofthewindingof relay 3041Y is such that the lampi 6 will remain lighted.Relay 304, however,

operates `and closes an obvious circuit for tlic lay 310 in operatingcloses an obvious VVcir- Aoperation of slow-to-operate relay 310.`Rccuit for the operation of s low-to-operate re- Y lay 311. Relay 311 inoperating extends the circuit previously traced4 through-'the winding ofrelayv30ll` directly to battery at the armature and front contact .ofthis relay, thus permitting relay 3011` to i'elease. Direct battery istherefore connected topshunt the guard and disconnect lamp 6extinguishing it by the vlow resistance winding of relay 15. On therelease vof relay 304 relays310 rand A311v release in succession tocause relay 304. to again be actuated and cause relay 306 to be `againlighted. `.This process of connecting and disconnecting direct batteryto the lamp circuit causes it to be periodically flashed to indicatc'tothe toll operator that her telephone set is connected vto the trunk Af iThe vconnection of the operators telephone lead 13 vbythe sequencecircuit, as previously mentioned-,causes theope'ration of 'Isetv'randthe sending of the tone signal to .the operator at ythe distant endofti'i'ink A will now be described.l Theextension of relay 313 overacircuit as follows: Battery,

lowerright-hand winding of repeating coil 19 of trunk A, winding ofsupervisory relay 20, lower outer armature and front Contact of relay 8,inner left-hand armature and front contact of relay 308, winding ofrelay Y. 13o

3-13 to ground. Relay 313 is of high resistbe made ofthe functioning ,ofparty line.

l equipment 24, or the operations in the truck Y i circuit whenthe'party answers the calle.

.Y .If troubleshould develop in the automatic listening Vcircuitequipment, the einergency listenindcircuit is ein lo ed to send'thelre-` n p quired tone trunk signal to the operator at Vthe distant -lendoli: the trunk Annd kto conneet thertoll operators'telephone set tothedisabled trunk. The lirst operation in this case will be to insert plug22 into jack 35 of kthe ei'iiergencyY listening circuit'shown in Y Fig.2 which, as indicated, is associated with ,the control circuit shown in3. The irstfeiect of this connection will be'the operation of rela-y 202andthe supervisory relay 20 over a circuit as follows.: Battery,

lower'rightdiand winding of repeating coil 19,'w1nding of supervisoryielay 20, lower armature and back contact of relay 26, ring terminals ofplug 22 vand jack 35;A left-hand inner armature and back: contact Aofrelay L203,V windingfotrelay 202,v innerleft-hand niakefbefore-Ybrealr.contacts of relay Y 205,`

rightfhandarniaturei and front contact of relay,307to ground. `The,operation ot' relay 202 .causes the operation or' relay 206 over anobvious circuit and-the operation of relay 206 closes a circuit for thelightingV of lamp 6 tand the operation-orl the sleeve relays il and 208overV a circuitV as. follows: Battery,A lainp 6, ,upper 'winding ofrelay 4, sleeve terminals of plug 22'y and jack-35, vwinding' ol relay208, innerV leftfhand)arinaturerand lfront contact of relay 202,right-hand arinature and front contacts i of relay 20GY to groundy Theoperation of relay 208 closes f an obvious circuit for relay 200 whichrelay incoperating opens the connections from the sequence circuit'tothe' control circuitso as f tornprevent vthe operation Y of thecontrol "circuit inthe usualV inanner. Relay 208 provides a-lockingcircuit .for itself'fand for the ,relay 4through its innerright-hand.arn'1a' Vture and front contactto 'ground at theouterfleftfhand `armature and' back VContact off-rela'y205. Relay 208alsocloses anobvioustcircuit for ,the operation of relay 209,

. the.V purpose of which will be described here-V inafter;A Theoperation of the'sleeve relay zLinthe trunk Vcircuitcauses the relay 2to 7 be released and the relcaseot this relay shunts the lainp 6 sothatthis vlamp isl now extinguished. AThatisl` a circuit is closedv fortheV operation of relay.V 26` as itollows: Bat-` ter 1, windinoot' relal20VV armature and back 2D Y 7 Y contact lof; rela-y 27,"z,1riiiature'`and .back

`contact of v-relay 2S, lower armatureV and V' front contact ofrclay 4,-outeiright-hand arinature and back contact of relay 2, outer yright-hand armature and front contact ot vrelay '3, upper winding ofrelay 4', winding ofrelay 208 to ground at the outer left-hand armatureand back contact of relay 205. `The operation of relay-26 connects theringing trip relay 28 to thevring conductor through`V a, key, as willbemore fully explained latelyy and Yopens the circuit tor the Ysupervisoryre` lay 20 and relay 202 in releasing releases re- `lay 206. Y g Itshould be noted that the operation Aet the above mentioned relays takes4a compara# tively shortvltin'ie so that theinonientaryf10pveration ofVrelay 20Y will not have any effect on the circuits atthey oppositeendof trunk A, in other words, it relay 20 is operated un.

der ordinary circumstances when the wantedV ysubscriber answers, theellfect would .be to charge a toll connection to the calling subscriber.In thiscase, however, the meinen.-

tary operation Vof the supervisory relay will have nosuch effect as itis of, a very Vshort duration. f1

As is well known in the, art' ot*` party line ringing, one of the partyline keys in equipment 2tis always operated. The'g'effect in thiscircuit from such operations will be as follows: For eXample,'il'"key Misffoperated a connection to ground will` beinade to the tip conductorot .trunk A and the genmade to the ring conductor oft trunk A.: In

this case therefore the groundconnection-ntoy the tip vconductorwillcause the operation conductor will be opened at the inner upperr-arinature of relay 203 aslhereinafter described. The operation of`relay, 210 closes obvious circuits for the operation of relays 203 and213 and these Vvrelays are held operated'by vthe ground connection at`the front `contacts andi thel outer yright-hand armature of 'relay 208through the arina' ture' and Airont Contact of Vrelay r213.- ItV Vwillbe noted that on the operation of relay 9e f eratorfor silent batteryconnection will be ico 206 a circuit is closed"forfrelay2l5. *OnV theL Yoperation of relay2l5-anrobvious circuit is closed for the operationo'fvrelay2l6. 'Relay 216, in operating, opens the eii'ergizing`cir-v4 cuitfor relay v215 and a circuitwill therefore be completed v'from ground,through the inakebc-ore-break contacts of relay 215 and the left-'handarmature and 4'l'rcnt contact or Arelay 216, but due to the factthatrelay 215' is slow tomrelease and relay 216r is lslow to operate,this connectionl` cannottherefore have any eiect before it is againopened at the operation of relay 203 and as relay 206 will be releasedon the release of relay 202 relay 216 will be presently released; lTherelease of relay 206 will of coursealso cause the release of relay 210,whilerelays 203and 213 are heldv 'operated as previously described. The,release of relay`206, however,

does not affect the operation of relayl 208 as it is now held operatedthrough the ground supplied at the outer right-handV armature and frontContact of relay 203, in addition to the locking circuit through 'theouter. left armature andrba'ck Contact of re-v hanrlarinature and backcontact of relay 211, Winding of relay 218inner right-,hand

armature and front contact of relay 203,r ing terminals of jack and plug22, lower armature and front-contact of relay 26, lower normalcontactsof key J and upper` normal lcontacts .of key 12V, upper madevcontacts of key M, Winding; of tripping relay 28, through theVright-,hand armature and lback Contact of relay 32 -to the source ofringing Current` Thev-circuit completed over the path just traced causesthe operation of .relay 218 and this relay, in operating, closes acircuit for'tl'ie operation of; relay 220 as followsz.

Y j Battery,- winding of relay 220, armature and` front contact of relay218, armature and front contact of relay 209to ground. It Will beremembered that the relai/'209 was operated on the operation of relay208.V `Relay 220 in operating,-provides a locking circuit for itselfthrough its innerright-hand armavture yand front Contact of relay 209inde-V pendent of the original energizing circuit for this relay throughthe armature and front Contact of relay 218. Y Y Y The operation ofrelay 220 closes an obviou-s energizing circuit for relay 211', whichinoperating, closes an obvious'locking circuit for itself through theouter right-hand Y armature and front contact of relay.. 2 08.` `Gir4the operation of relay 211, the energizing circuit for relay 209 is'opened at the outer right--hand armati'ire and back Y contact of thisrelay and Vrelay 209 is released, but as this relay is slow to releaseit will maintain relay-'220 operated forashort'peri'od after rel-,133211is operated soy that a momentary circuit will be completed for theopera-tion of the .tripping relay 28 as follows: Battery, through ltheouter rightfhan'd armature and front contact of 'relay 220, outerlelt-liand armature andv front contact of relafy"211, ring terminals ofjack 35 and plug f' '22, lower armature and. front contact of vrelaly26', lower normal contacts of key J, Vupper normal-,contacts of key W,upper made contacts of key M, Windingof tripping ren lay 28, rightehandarmature anc'lbackeoib` tact of relay 32 to ringing source 34.. `Thisconnection directly to battery atpthe outer right-'hand armature andfront contae'tofref zol lay 220 is'suchj that 'the tripping relay 28will be actuated as is, Wellknown in the art,

The opera-tion of relay28 opensjthe short circuit for the windingofr'elay 27 through l y the armatures andback contacts of relays 28 and2f( and relay 27 will now therefore ovp- I eratey in series with' relay26.V The operation of relay 27, in turn establishes a shortci-r-A vcuiting connection to battery for relayv 26,1

which is thereby released.

relay 2T remains' operated.` By tliistime yre` lay 211 is` operated toopen the original en,- ergizing circuitfjfor relay`r2f8, and as relays209,218 4and,220v have released the supei-, yisoryielay 20'cannot-be'again operatedas long as the connection 7to the einergencyrlisteningcircuit is maintained,

'llliei'eleasegof the relay 220 and relay 205 as follows:;BatteryWinding-of l The releaseV relay26 opens the circuitfor relay 28whichgisnow released, Whereas' the'f'inain--l tenance ot relay A211V operatedcauses Va cirv cuit to be conjipleted-.forthe operation ofl relay 205,middle right-hand armature and" back contact of relay 220, innerleft-hand-` armature and front contact of relay 211 to ground;v Relay205, in operating, completes the tip conductor connection at itsvright,-

trol'lircuit shown'in r`Fig. 3 and the 'fact that relay 211 is operatedVand'ielay, 220 is released causes theconneotion from thering conductorYtorlue also completed to 'the con- `hand armature andfrontcontact totheeontrol circuit. rElie/operation of relay205` alsoV A provides aground connection atit'souter niake-before-break contacts through the inneil leftfhand armature andzback contactof vrelay-223 for-vtheiop-eration of relay ,315 in the control circuitl The'oper'ation ofrelay 315 causes, ashereinbefore. described, `the control circuity tofunction to Iapply tone to the trunkr and thereafter to connect theoperators telep'lioneset 300`to the trunk'AL' 'l The toll operator willnowreceive the deysired information from the operator at'the distant endof the, \tru`nkA and when `r'this informationjis received, lsheWillfreinove the ,plug 22 from Vjaok' of the emergencylis-v teningcircuit andr insert this ,plug into the:

jack of the desired subscribers'line. VThe removal of plug 22 from jack35' causes the Virelease of theoperated Vrelays inthe einer.

gency listen-ing circuit as follows, thatis', relay 208 isv firstreleased ,andl this relay,`in

turn, 'releases` relay 213, 203, 211, v'205 and 20o.v f f to ringconductor from the source 36e-nd ground on the tip conductor. AIn thisease nity W is Operated apne @may i 'y battery or' silent intervalbattery is applied i tlievoperation of the .circuit would be the'samefas hereinbefore described.V n the j other hand, if either key JorleyR isoperatedground will be connected to therin'g conductor andbattery and silent interval "battery of this character connected vto the208 andr from thereon the operations ol-theVA Y circuit Awill beV twocases.

' y tipconductor. Y In this case relay 202 will release and relays 203and 213 beoperated through the right handarmature and back contact ofrelay 202 'from groundat relay the 4same'as in the previous Referringlnow,l tothe operation of the emergency listening circuit when used inconnection with a toll'switcliilig trunk suchv asis shownin Fig.4.Itshould be mentioned inithis connection that Ytheiiunctions forautomatically transmitting, throughthe control circuit shown in VFigs.`V2 andl 3, a tone signalto theoperator at the distant l endof'ajtoll'-switching trunk- B and .i'or subsequently*connecting theoperators telepreviously described in connection with. the A, B ortandemcompleting trunk A. `It'is 'when the toll switchingftrunk B isjtakenA phone, inV this case toll switching operator, are practicallyidentical with the operations therefore, Vonly necessaryl to brieflyvoutline V"the functions relating totheseizing of the trunk B. Y

"Assuming'then that rela; 400 is operated :for use,` a circuit `Will becompleted for the operation `ofrelay 402 as follows; Righthand windingof relay 402, .inner right-hand .armature andback Contact of relay 403,ar-

mature and iront Vcontact of relay 400 vto ground. The operation'of thisrelay closes a circuit for the operation ofrelays 403 and y404V asfollows: Battery, left-hand Vwinding` of relay 403, left-hand windingoi' relay 402, outer leftdiand armature and front contact of relay 402,lower` outerarmature andjbacl contact 'of relay 415, right-hand windingo i relay' 404 to ground. Relay 404v in operating `,closes an obviousholding circuit Vlor relay f '7 400 and opens the connectionsfrombattery land 4ground to Vthe trunk B throughlvthe Atrunk hasnoleffect at;this

`Windingsof relay 400. As is well known the removalof thehatteryandground from the Y l time at the distant end of the trunk. 'i

Y y Relay 403 in. -operatingl closesl a *locking y circuitf for itselfunder 'control of relay 400 and completes an obvious circuit `forthelighting ofV lamp 406. This relay also com.g

I .pletes 4the connections for conductors 409, 410 and 411 to thesequence circuit inthe same manner as the .connections for con'- ductors9,10 and 11 werecompleted-to the sequence circuiti from trunk A in Fig.1.v

Thegautomatic,connection of the toll switchf ing operators telephone setand the transmission of the ktone signal tothe distant end" volifV thetrunk is accomplished in the same manner as' in the-case oi' trunk vAhereinbe fore described.

It trouble should develop in the automatic listening circuit equipmentthe emergency listening circuit Vwill, be employed to Vsend the requiredtone signal tothe operator at the `distant end et trunk B and to connectthe' toll switching operators telephone set to this trunk.` T he iirstoperation in this casewill be to insert plug 422 into jack 435 thatmay-be considered as the equivalent of jack 35. The effect of thisconnection Ywill be the operation of relay 202fand the supervisory relay420 over `a circuit as follows: Battery, winding of relay 420, lowerright-hand Winding of repeating coil 419, lower outer armature'and'bacl;contact of relay 426, ring ter-v mina-ls of plug 422 and jack435, innerrighthand armature and back contact'of relay 203,

l Winding o1'- relay 202,V inner left-hand make# before-break contactsotrelay 205, righthand armaturel and iront cont-act of relay 307 f.

to ground. The operation Vof relay 202 causes` Athe operation ofrelay'206` overan obvious circuit. i The operation. 01"' relay 206closesv aV circuit for the lighting of lamp 406 'andV the f operationofsleeve relays V415 and 208 overa Y v A, circuit asiiollows: Battery,winding of `r'e-V lay 415, sleeve terminals-of plug 422'jand jack'435,winding `off-relay 208, inner left# hand'armature' and front contact ofrelay 202, right-ha`nd armature andfront contacts oit-relay 206 toground,y The operation of relay 208 closesl an obvious circuit for relay200 which relay in operating opens the connecticns'from the sequencecircuit to the control circuit so as to prevent the operation of theautomatic listening circuit in the usual manner. Relay 206 provides aloclingicircuit for itself and tor relay 415 through its innerright-hand armaturev and frontY con- .tact Vto ground at the outerleft-hand armature and back Contact of relayv 205. Relay 208 also closesan obvious rcircuit for the operationof relay 209, This relay serves-nouseful purpose in this type of connection The operation of relay 206also completes a` circuit from Vbattery and groundr through 'resistancesand the lefthand armature and `1lront Vcontacts otrelay206 through thewinding of relay 210, the inner yleft-hand armaimi ture and back contactvrofrelay 203, right-zV hand armature and back contact of relay 205,through the tip conductor on the'trunlr` circuit-connectionydistinguishes the operau` v tions as follows .from the Aoperations whenthe AB or tandem completing trunks are connected to the emergencylistening circuit.

VThe operating of relay 206 also completes an obvious circuit-fortheoperation ofL relay 215- which in' operation closes an obviouscircuitfor the operationof relay 216. On the operation of relay 216 thevorigina-l .energizing circuit vfor relay 215 is opened and .this relayis now released. Relay 216 is 7 slow-to-operate and relay 215 isslow-torelease, hence the circuit from the ground at themake-before-break contacts of relay 215 through the` left-hand armatureand front contact of relay 216 is delayed for a` short period althoughthis is of no importance in connected toa toll switching trunk, butV asVthisfcase.A That is, this delay in completing Vthe above-circuitthroughthearmatures and contacts ofrelays 215 and216 is not requiredwhen the emergency listening circults are previously stated, it. wasnecessary to introduce 4'this delay when the emergencyv listen'- ingcircuit was connected to an AB lor tandem com )letino trunk in yorder torevent any effects in the circuits from this connecductor through toouter right-hand armature ofrelay 220. This relay also in operatingopens at its middle left-hand armature and back Contact the circuit forrelay 218 which is not used in this case but was employed in theprevious case to cause the tripping of ther-inging equipment. Relay 211in oper-V ating closes an obvious lockingcircuit lfor itself undercontrol of relay 208 and opens the circuit for relay 209 which is nowreleased. Another circuit completed-by the l operation of relay 211 isone for theroperation of relay 205 as follows: Battery, y'windkj ing ofrelay 205, middle righthand armaturea-nd back contact of relay 220,inner left-hand armature and frontcontact of relay 211'toground.

rRelay 205 in operatingV disconnects the relay 210 from t-hetip side ofthe connection and bridges relay 202 across the tip and' ring conductorsas follows: The tip conductor of Y the emergency listening circuit,inner lefthand armature and front contact of )relay 205, wind-ingofrelay 202, inner left-hand armatureand back contact of relay 203 to thering conductor.` It should be reinem-l bered Vthat, the supervisoryrelay 420 Wasl ope-rated` on the insertion of plug l422 into jack 435through the inner left-handmakebefore-break contacts of relay 205. Thecir-y cuit for this relay will now, due lto the oper- I.

ation of relay 205,v eXtend throughfthe wind;- ing of relay` 202, theinner left-hand armature and front contact of relay 205, the tipconductors of the emergency listeningcircuit and the toll switchingtrunk`through the upper right-hand winding of repeats ing coilV 419 to groundso that the -super` visory relay will, even though the above mentionedchanges have taken place inthe emergency' listening circuit, bemaintained operated as long as this; circuitconnection remains; This isin orderto prevent any effects from the connection of the emergencylistening circuit to the Itoll swtchingtrunk from being transmittedtothe distant lend of trunk B which would ordinarily be pro-y ducedonthe operation of-thefsleeve rel-ay f 415.' It will be observed thatyon the operation of relay 415 the original energizing cir;

esl

cuit for relay^404 is opened at V,the lower v outer armature andbackzcontact ofthis relay,k so that under `ordinary circumstances whenplug 422'is insertedin `the jackofthel wanted subscribes'v line theyoperation -of 9e l this relay 415 and the release of relay 404 Y wouldconnect battery Vand ground across the i been extended to the wantedsubscriber and that hemay be rung'. f ln this case therefore ythiseffectis not transmitted as relay 404 is lmaintained operated due to theoperation of the supervisory relay 420. The. circuit for maintainingrelay 404 operated may be traced as -follows: Battery, left-hand windfing of relay 404, arn'iature and front contact ofv supervisory relay420, armature and front contact .of relay 400 to ground. v

The operation of relay 205 also completes a. circuit from ground vat itsleft-hand outer make-before-break contacts th'roughthe in-4 nerright-hand armature and frontlcontact of relay 283for thev operation'ofrelay 315 in the control vcir-cuit.

to transmit the tonesignals to the" distant .end of lthe'trunk B andconnect theopei'a- The operation'of this i y p relay starts lthe controlcircuit to function tors telephone set 300 to the trunk in aman@r nerashereinbefore described/except thatlthe connection extends through jack435. f

f 'VVhen'the toll switching operatorV receives l Athe number of thewanted* subscriber'from the operator `at'the distantend of trunk B1 shewill remove plug 422 from jack 435 and insert the plug into jack 423 ofthe want-ed be completed as in th'efordinaryk way.. VThe Y subscribersli'ne and the connection will then y remo-val of the plug from jack 435causes i the release in the emergency llistening circuit of the relaysthat were operated, name- 1y; Relayseoa 20s, 200, 206,216, 211 andAnother means is 'provided in this circuit arrangement 'for suspending,automaticV lis" tening for the trunks. This means is the key 230. It therelays for transmitting` the tone to the distant, end 'of the connectedtrunk are functioningV properly the key 230 is operated to the right.This closes an ob vious .circuit for the operation ot relay 231. Relay231 in operating` closes accircuitifoi the operation ot relay 200 asfollows: Battery, windingV of relay 200, armature and front Contact ofrelay i331, right-hand armature and front `contact o't relay-l 307 toground.Y The operation ot' relay 2O0Vfunctions ashereinbetore stated toopen thecon y i'iectioni from the sequence circuit to a con-K trolcircuit to make ,the automatic listening equipment. inoperative; V i ylfltherelays lfortransmitting the tone are not functioning properly .orare to be tested the key 230 is. operated to the'lett. This operation ofkey V230 closes an obvious circuit for relay 233.: ,Relay 233inoperating performs the saineiunction fas relay 231,

thatfisi, it Vcloses a Vcircuit iorvthe operation of relay 200 and in`addition bridges the talkingv leads aci'ossjtlie two outer rightl y handarmatures of the last tonesrelaytle,

thus Vproviding a means lor connecting 'the operator to the trunkwhilefthe tone signal p. requipment. is being tested.y The lead-'tronixtrunks of different character arranged to Y transmit a signal duringthe. connection ot a Y ".lhat is claimed is:

theA left-hand outer -n'iake-betore-break-:con-

.tacts and relay 205 for the startingpofitlie tone signal Aequipmentat*the'roperationfoii ithisrelay in case the .emergency listeningcircuit is Yinadvertently usedV is opened by the operation ofrelayr223-y Y Y It'should be understood'that the invention is notlimited inits use to trunks ot these particular types but'inay beapplied Vin Lany other suitable manner to other trunks oi similarCharacteristics in regard Y to K the pre- Vention Vot disturbances intrunk connec- :tions during the luse ot an emergency listeir ing'circuiti Y.

l. In a telephone system, subscribers lines',

subscribers line thereto, and a listening ci i'- cuit including amarginally responsive de`- vice for Ydifferentiating between saiddifferL entV character trunks, means vcoac'ting with sai'ddevice whenthe listening circuit is coiinected to a trunk of a certaincharacter toi prevent 'the transmission of a signal rby said trunk, and meanscoacting witlrsaid device wlienthe listening circuit V.is connected to a-trunk. of ay differentv character to prevent the transmission oit asignal by said second men tioned trunk. y 1

2. In aftelephone system, subscribers lines, trunks v,of differenticharacter, Veach *includ- Lenin-azieV inga supervisory relayarranged tobe operA ated to' tran-smit a signal when the sub-V scriber on the lineconnected to the trunk answers a call, and a Vlistening circuit ar-Vranged when :connectedpto a trunkof one characterto actuate thecorresponding su-l pervisory relay as long as the listening circuitisconnected to the ti'unk to prevent the transmission of a signal,andarrangedwhen subscribers line thereto,` an automatic lis-v teningcircuit includinganf operators tele-` phone set arranged to belconnected. to a trunk in response to. the seizure Voi said trunk, ineansfor independently connecting said operators telephone set to a` trunkfor disabling the automatic listeningcircuit and for preventing thetransmission of a signalV byy said trunk,`regardless of its character inresponse to` the association of saidmeans with said trunk'.` Y

e. in a telephone system, trunks of diffen. ent character, subscriberslines, an automatic listening circuit including an operatoi-s telephoneset and, a tone producing equipment, means responsive to the seizure ofa trunk for actuating said automaticy lis-vV tening circuit to transmita tone signalover said trunk and connect the operators telephone settosaid-trunk, means Vtor connectiiig'aL trunk to a subscribers line, asource ot ringing, current, means responsive dur,-

'ing the oon'nectionofa subscribersline to a trunk l'or rendering saidsource effective, any

emergency listening circuit associated with saidgautomatic listeningcircuit, means for Y connecting said emergency listening-circuit toatrunk, means responsive to such acoii-A Y nection for preventing Vthenormal Vunctions of the automatic listening circuit and actuating it` to`transmit a tone signal through the emergencylistening circuit to theconnected trunk, means to connect the operators telephone set throughtheemergency listening circuit to the connected trunk, and means. in

said'eniergency listening circuit for prevent ing the transmission of aVringing' signal,

over the trunk Awhenpthe emergency listening circuit is connectedthereto, regardless ot the character oil'I the vconnected trunk.

Inl witness whereof, I. hereunto subscribe my naine tliis-'lthdayofOctober, A. D. 1926. L i

WILEY, WHITNEY@

